In thesis

Vallin, Adrian

Stockholm University, Faculty of Science, Department of Zoology.

2006 (English)Doctoral thesis, comprehensive summary (Other academic)

Abstract [en]

Eyespots, circular patterns which resemble the general appearance of the vertebrate eye, are widespread throughout the animal kingdom and are for example, commonly found on the wings of butterflies where they have been proposed to confer protection against predation. However, empirical evidence of the adaptive value of eyespots, as well as knowledge of butterfly behaviour under the threat of predation, is scarce. In Paper I, we subjected three butterfly species to attacks by insect eating birds. Results show that, although being closely related, these three species have developed fundamentally different kinds of anti-predation adaptations. Paper II demonstrates that the conspicuous eyespots, in combination with the wing-flicking of peacock butterflies, Inachis io, provide efficient defence against blue tits, Parus caeruleus. Peacocks appear to be edible to blue tits, thus, this is an example of effective animal defence by bluffing. During winter hibernation however, Paper III suggests that adult peacock butterflies do not survive predation better compared with its close relative the small tortoiseshell, Aglais urticae, a species lacking eyespots. In Paper IV we argue that two edible insect species carrying equally large eyespots are not necessarily equally well protected against bird predation. In this study, a higher frequency of the larger prey, the eyed hawkmoth, Smerinthus ocellatus, were killed compared with the smaller prey, the peacock butterfly. Finally, Paper V shows that birds approach emperor moths, Saturnia pavonia, a species always exposing their eyespots, earlier after the onset of a trial, compared with eyed hawkmoths, a species hiding their eyespots until harassed by a bird. This suggests that large eyespots may catch the attention of a nearby predator and in situations where predators are not intimidated by the display, eyespots may switch from being potentially beneficial to being a costly trait.